Direct evidence for anisotropic magnetic interaction in $\alpha$-RuCl$_3$ from polarized inelastic neutron scattering

TL;DR

Polarized neutron scattering reveals anisotropic magnetic correlations in $ ext{RuCl}_3$, providing direct evidence of bond-directional interactions and challenging simple Heisenberg or pure Kitaev models.

Contribution

This study provides direct experimental evidence of anisotropic magnetic interactions in $ ext{RuCl}_3$ using polarized neutron scattering, highlighting complexities beyond simple models.

Findings

Anisotropic magnetic correlations observed in $ ext{RuCl}_3$

Opposite anisotropy of inelastic response to simple Heisenberg expectations

Absence of low-energy transversal magnon modes near antiferromagnetic q-vector

Abstract

Polarized neutron scattering experiments reveal the anisotropy of magnetic correlations in the candidate Kitaev material $\alpha$-RuCl$_3$. The anisotropy of the inelastic response at the magnetic Bragg positions is just opposite to the expectation for a simple Heisenberg model. Near the antiferromagnetic $q$ vector, there are no low-energy transversal magnon modes directly documenting the fully anisotropic and bond-directional character of the magnetic interaction in $\alpha$-RuCl$_3$. However, other findings disagree with a simple or strongly dominant Kitaev component.